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¹ Mahathma Ghandi University, Letha P Cheriyan, Post Graduate and Research Department of Zoology Mar Thoma College, Tiruvalla, Kerala
² Catholicate College Pathanamthitta affiliated to Mahathma Gandhi University, Research and Post Graduate Department Of Zoology, Kerala
³ Transdisciplinary Biology Group, Rajiv Gandhi Center for Biotechnology, An Autonomous institute of the Department of Biotechnology, Government of India DOI : 10.4194/GA543 Viewed : 1603 - Downloaded : 1000 Meenachil River is the only river originating from Southern Western Ghats of India having human settlement right from the headwaters to the mouth. The river is subjected to human-induced stressors to varying extents, resulting in a drastic decline in riverine health and fish diversity. The population genetic structure of two species commonly distributed in different geographical zones of Meenachil River, Dawkinsia filamentosa and Pseudetroplus maculatus were studied using the 16S mitochondrial ribosomal RNA gene sequences. Haplotype clustering and the presence of unique haplotypes were identified by phylogenetic and network analysis. Six haplotypes were identified for D. filamentosa and ten for P. maculatus. The neutrality estimations of the upstream and midstream populations of the species revealed the presence of an excess of common alleles with neutral mutations indicating a population expansion after bottleneck and stabilizing selection. The downstream population revealed the presence of an excess of rare alleles with non-neutral mutations indicating a positive directional selection and population sub-division. Population expansion demonstrated star-like phylogenies with rare haplotypes separated by mutational steps from the ancestral haplotypes. The private haplotypes indicated the existence of selection pressure in the downstream zone of the river. Keywords : Fishes, Diversity Haplotypes Non-neutral mutations Directional selection